Carbon nanotubes can be classified by the number of walls in the tube, single-wall, double wall and multiwall. Carbon nanotubes are currently manufactured as agglomerated nanotube balls, bundles or forests attached to substrates. Use of carbon nanotubes as a reinforcing agent in elastomeric, thermoplastic or thermoset polymer composites is an area in which carbon nanotubes are predicted to have significant utility. However, utilization of carbon nanotubes in these applications has been hampered due to the general inability to reliably produce individualized carbon nanotubes and the ability to disperse the individualized carbon nanotubes in a polymer matrix. Bosnyak et al., in various patent applications (e.g., US 2012-0183770 A1 and US 2011-0294013 A1), have made discrete carbon nanotubes through judicious and substantially simultaneous use of oxidation and shear forces, thereby oxidizing both the inner and outer surface of the nanotubes, typically to approximately the same oxidation level on the inner and outer surfaces, resulting in individual or discrete tubes.
The present invention differs from those earlier Bosnyak et al. applications and disclosures. The present invention describes a composition of discrete, individualized carbon nanotubes having targeted, or selective, oxidation levels and/or content on the exterior and/or interior of the tube walls. Such novel carbon nanotubes can have little to no inner tube surface oxidation, or differing amounts and/or types of oxidation between the tubes' inner and outer surfaces. These new discrete tubes are useful in many applications, including plasticizers, which can then be used as an additive in compounding and formulation of elastomeric, thermoplastic and thermoset composite for improvement of mechanical, electrical and thermal properties.
Other useful applications include electromagnetic interference (EMI) and radio frequency interference (RFI) shielding applications. Currently, there are many developments in the electronics industry that require devices (e.g. phones and laptops) to operate in the 1 GHz-14 GHz frequency range to keep up with the high demands of data transport. Electromagnetic interference (EMI) is a disturbance by an external source that affects the electrical circuit, or vice versa. Electromagnetic shielding is a process which reduces the transmission of electromagnetic radiation interfering with the electronic circuits. The EMI shielding effectiveness (SE) is measured in decibel (dB) and can be expressed in terms of attenuation of power.SE=10 log(Pi/Pt)with Pi the incoming power and Pt the transmitted power. SE is the sum of three processes: reflection, absorption and multiple reflection of the incoming electromagnetic wave. The reflection of the radiation is due to the mobile charge carriers (electrons and/or holes) interacting with the electromagnetic field. Absorption requires the material to have electric or magnetic dipoles which interact with the electromagnetic field. Multiple reflection occurs when the radiation transverses two or more reflection interfaces.
Metals are known for their high EMI shielding effectiveness due to reflection of the radiation, but are not a good material for applications such as mobile phones due to their weight, heat entrapment and potential for corrosion. Thin metal coatings also mostly reflect and with many circuits close together, issues can arise from cross-talk. An increasing preference is for EMI shielding materials that absorb rather than reflect. Carbon-based polymer composites as enclosures are most promising as light-weight, high strength composites with some shielding capability which can be augmented by metal flakes or fibers. However, in these discontinuous phase metal/carbon fiber based composites, the shielding effectiveness decreases rapidly with increasing frequency above 2 GHz such that ˜−10 dB/cm values are common and these composites also have relatively small absorbing characteristics. As electronic components increase in complexity and miniaturization it is increasingly difficult to shield via metallic enclosures.
In general, metals like iron, chromium, aluminum, uranium, platinum, copper, cobalt, lithium and nickel are magnetic in nature. Certain rare earth metals such as neodymium, samarium can form alloys for very strong permanent magnets. Their metallic compounds and alloys, sometimes with various metals are also magnetic in nature. For example of an oxide compound, the formation of magnetite, Fe3O4, happens through reaction: Fe2++2Fe3++8OH−→2Fe3O4+4H2O. Magnetic particles of diameter greater than about 1 micrometer, such as iron oxide Fe3O4, magnetite, are used at high loadings, for example greater than 70% weight in a silicone or acrylic medium. These have good absorbing characteristics above about 6 GHz, typically reaching −150 dB/cm at 25 GHz, but are of density typically greater than 4 g/ml and of low strength or tear resistance. The handleability can be so poor that often plastic sheets are used on their surfaces to provide handleability without fracture. Thus, there is a large, unmet need for wider broadband (2-50 GHz) highly absorbing materials with good strength or tear resistance giving rise to improved handleability.
A further improvement in the absorption characteristics of magnetic particles at frequencies less than 6 GHz, although not limited by this frequency range, is anticipated with particles less than a certain diameter such that superparamagnetism is observed. Superparamagnetic materials are so small that they consist of only one magnetic domain. For this reason, they are believed to be much more susceptible to absorb energy from an external electromagnetic field compared to the same composition but with micrometer and above diameter particles which consist of multiple magnetic domains, since these multiple domains will not only interfere with the external electromagnetic field, but also with each other. Typical diameters of particles that exhibit superparamagnetism are less than 70 nanometers. However, these nanoscale particles are often very difficult to disperse in their elementary particle state and larger scale agglomerations often lead to reductions in the strength of the composite. Thus, there is a need for improved dispersion of the elementary magnetic particles of diameter less than about 70 nanometers in the host liquid matrix at room temperature such as, but not limited to, silicone. or a solid matrix at room temperature such as, but not limited to, a thermoplastic or thermoset polymer.
One embodiment of the present invention is a electromagnetic shielding composition comprising a plurality of discrete carbon nanotubes and at least one magnetic metal and/or alloy thereof, wherein the discrete carbon nanotubes comprise an interior and exterior surface, each surface comprising an interior surface oxidized species content and an exterior surface oxidized species content, wherein the interior surface oxidized species content differs from the exterior surface oxidized species content by at least 20%, and as high as 100%, preferably wherein the interior surface oxidized species content is less than the exterior surface oxidized species content.
The interior surface oxidized species content can be up to 3 weight percent relative to carbon nanotube weight, preferably from about 0.01 to about 3 weight percent relative to carbon nanotube weight, more preferably from about 0.01 to about 2, most preferably from about 0.01 to about 0.8. Especially preferred interior surface oxidized species content is from zero to about 0.01 weight percent relative to carbon nanotube weight.
The exterior surface oxidized species content can be from about 1 to about 6 weight percent relative to carbon nanotube weight, preferably from about 1 to about 4, more preferably from about 1 to about 2 weight percent relative to carbon nanotube weight. This is determined by comparing the exterior oxidized species content for a given plurality of nanotubes against the total weight of that plurality of nanotubes.
The interior and exterior surface oxidized species content totals can be from about 1 to about 9 weight percent relative to carbon nanotube weight.
Another embodiment of the invention is an electromagnetic shielding composition comprising a plurality of discrete carbon nanotubes and at least one magnetic metal and/or alloy thereof, wherein the discrete carbon nanotubes comprise an interior and exterior surface, each surface comprising an interior surface and an exterior surface oxidized species content, wherein the interior surface oxidized species content comprises from about 0.01 to less than about 0.8 percent relative to carbon nanotube weight and the exterior surface oxidized species content comprises more than about 1.2 to about 3 percent relative to carbon nanotube weight.
The discrete carbon nanotubes of either composition embodiment above preferably comprise a plurality of open ended tubes, more preferably the plurality of discrete carbon nanotubes comprise a plurality of open ended tubes. The discrete carbon nanotubes of either composition embodiment above are especially preferred wherein the inner and outer surface oxidation difference is at least about 0.2 weight percent.
The compositions described herein can be used as an ion transport. Various species or classes of compounds/drugs/chemicals which demonstrate this ion transport effect can be used, including ionic, some non-ionic compounds, hydrophobic or hydrophilic compounds.
The new carbon nanotubes and at least one magnetic metal and/or alloy thereof disclosed herein are also useful in ground water remediation.
In all of the uses disclosed herein, the magnetic metal and/or alloy thereof is selected from the group consisting of iron, chromium, aluminum, uranium, platinum, copper, cobalt, lithium, nickel, neodymium, and samarium. The magnetic metal and/or alloy thereof preferably comprises a metal and/or alloy oxide.
The compositions comprising the novel discrete targeted oxidized carbon nanotubes and also be used as a component in, or as, a sensor.
The compositions disclosed herein can also be used as a component in, or as, drug delivery or controlled release formulations.
In some embodiments, the compositions disclosed herein can be used as a component in, or as, payload molecule delivery or drug delivery or controlled release formulations. In particular various drugs, including small molecule therapeutics, peptides, nucleic acids, or combinations thereof may be loaded onto nanotubes and delivered to specific locations. Discrete carbon nanotubes may be used to help small molecules/peptides/nucleic acids that are cell membrane impermeable or otherwise have difficulty crossing the cell membrane to pass through the cell membrane into the interior of a cell. Once the small molecule/peptide/nucleic acid has crossed the cell membrane, it may become significantly more effective. Small molecules are defined herein as having a molecular weight of about 500 Daltons or less.
The pro-apoptotic peptide KLAKLAK is known to be cell membrane impermeable. By loading the peptide onto discrete carbon nanotubes KLAKLAK is able to cross the cell membrane of LNCaP human prostate cancer cells and trigger apoptosis. The KLAKLAK-discrete carbon nanotube construct can lead to the apoptosis of up to 100% of targeted LNCaP human prostate cancer cells. Discrete carbon nanotubes may also be useful for delivering other small molecules/peptides/nucleic acids across the cell membranes of a wide variety of other cell types. Discrete carbon nanotubes may be arranged to have a high loading efficiency, thereby enabling the delivery of higher quantities of drugs or peptides. In some instances, this transport across the cell membrane may be accomplished without the need for targeting or permeation moieties to aid or enable the transport. In other instances, the discrete carbon nanotubes may be conjugated with a targeting moiety (ex. peptide, chemical ligand, antibody) in order to assist with the direction of a drug or small molecule/peptide/nucleic acid towards a specific target. Discrete carbon nanotubes alone are well tolerated and do not independently trigger apoptosis.
Peptides, small molecules, and nucleic acids and other drugs may be attached to the exterior of the discrete carbon nanotubes via Van der Waals, ionic, or covalent bonding. As discussed, the level of oxidation may be controlled in order to promote a specific interaction for a given drug or small molecule/peptide/nucleic acid. In some instances, drugs or peptides that are sufficiently small may localize to the interior of discrete carbon nanotubes. The process for filling the interior or discrete carbon nanotubes may take place at many temperatures, including at or below room temperature. In some instances, the discrete carbon nanotubes may be filled to capacity in as little as 60 minutes with both small and large molecule drugs.
The payload molecule can be selected from the group consisting of a drug molecule, a radiotracer molecule, a radiotherapy molecule, diagnostic imaging molecule, fluorescent tracer molecule, a protein molecule, and combinations thereof.
Exemplary types of payload molecules that may be covalently or non-covalently associated with the discrete functionalized carbon nanotubes disclosed herein may include, but are not limited to, proton pump inhibitors, H2-receptor antagonists, cytoprotectants, prostaglandin analogues, beta blockers, calcium channel blockers, diuretics, cardiac glycosides, antiarrhythmics, antianginals, vasoconstrictors, vasodilators, ACE inhibitors, angiotensin receptor blockers, alpha blockers, anticoagulants, antiplatelet drugs, fibrinolytics, hypolipidemic agents, statins, hypnotics, antipsychotics, antidepressants, monoamine oxidase inhibitors, selective serotonin reuptake inhibitors, antiemetics, anticonvulsants, anxiolytic, barbiturates, stimulants, amphetamines, benzodiazepines, dopamine antagonists, antihistamines, cholinergics, anticholinergics, emetics, cannabinoids, 5-HT antagonists, NSAIDs, opioids, bronchodilator, antiallergics, mucolytics, corticosteroids, beta-receptor antagonists, anticholinergics, steroids, androgens, antiandrogens, growth hormones, thyroid hormones, anti-thyroid drugs, vasopressin analogues, antibiotics, antifungals, antituberculous drugs, antimalarials, antiviral drugs, antiprotozoal drugs, radioprotectants, chemotherapy drugs, cytostatic drugs, and cytotoxic drugs such as paclitaxel.
Batteries comprising the compositions disclosed herein are also useful. Such batteries include lithium, nickel cadmium, or lead acid types.
Formulations comprising the compositions disclosed herein can further comprise an epoxy, a polyurethane, or an elastomer. Such formulations can be in the form of a dispersion. The formulations can also include nanoplate structures.
The compositions can further comprise at least one hydrophobic material in contact with at least one interior surface.
The present invention relates to a composition comprising a plurality of discrete carbon nanotubes and a plasticizer wherein the discrete carbon nanotubes have an aspect ratio of 10 to about 500, and wherein the carbon nanotubes are functionalized with oxygen species on their outermost wall surface. The discrete carbon nanotubes comprise an interior and exterior surface, each surface comprising an interior surface and exterior surface oxidized species content wherein the interior surface oxidized species content comprises from about 0.01 to less than about 0.8 percent relative to carbon nanotube weight and the exterior surface oxidized species content comprises more than about 1.2 to about 3 percent relative to carbon nanotube weight. The oxygen species can comprise carboxylic acids, phenols, or combinations thereof.
The composition can further comprise a plasticizer selected from the group consisting of dicarboxylic/tricarboxylic esters, timellitates, adipates, sebacates, maleates, glycols and polyethers, polymeric plasticizers, bio-based plasticizers and mixtures thereof. The composition can comprise plasticizers comprising a process oil selected from the group consisting of naphthenic oils, paraffin oils, paraben oils, aromatic oils, vegetable oils, seed oils, and mixtures thereof.
The composition can further comprise a plasticizer selected from the group of water immiscible solvents consisting of but not limited to zylene, pentane, methylethyle ketone, hexane, heptane, ethyl actetate, ethers, dicloromethane, dichloroethane, cyclohexane, chloroform, carbon tetrachloride, butyl acetate butanol, benzene or mixtures thereof.
In yet another embodiment the composition is further comprises an inorganic filler selected from the group consisting of silica, nano-clays, carbon black, graphene, glass fibers, and mixtures thereof.
In another embodiment the composition is in the form of free flowing particles.
In another embodiment, the composition comprises a plurality of discrete carbon nanotubes and a plasticizer wherein the discrete carbon nanotubes comprise from about 10 weight percent to about 90 weight percent, preferably 10 weight percent to 40 weight percent, most preferably 10 to 20 weight percent.
An another embodiment is a process to form a composition comprising discrete carbon nanotubes in a plasticizer comprising the steps of: a) selecting a plurality of discrete carbon nanotubes having an average aspect ratio of from about 10 to about 500, and an oxidative species content total level from about 1 to about 15% by weight, b) suspending the discrete carbon nanotubes in an aqueous medium (water) at a nanotube concentration from about 1% to about 10% by weight to form an aqueous medium/nanotube slurry, c) mixing the carbon nanotube/aqueous medium (e.g., water) slurry with at least one plasticizer at a temperature from about 30° C. to about 100° C. for sufficient time that the carbon nanotubes migrate from the water to the plasticizer to form a wet nanotube/plasticizer mixture, e) separating the water from the wet carbon nanotube/plasticizer mixture to form a dry nanotube/plasticizer mixture, and f) removing residual water from the dry nanotube/plasticizer mixture by drying from about 40° C. to about 120° C. to form an anhydrous nanotube/plasticizer mixture.
Another embodiment is the composition of discrete carbon nanotubes in a plasticizer further mixed with a least one rubber. The rubber can be natural or synthetic rubbers and is preferably selected from the from the group consisting of natural rubbers, polyisobutylene, polybutadiene and styrene-butadiene rubber, butyl rubber, polyisoprene, styrene-isoprene rubbers, styrene-isoprene rubbers, ethylene, propylene diene rubbers, silicones, polyurethanes, polyester-polyethers, hydrogenated and non-hydrogenated nitrile rubbers, halogen modified elastomers, flouro-elastomers, and combinations thereof.
Another embodiment is the composition of discrete carbon nanotubes in a plasticizer further mixed with at least one thermoplastic polymer or at least one thermoplastic elastomer. The thermoplastic can be selected from but is not limited to acrylics, polyamides, polyethylenes, polystyrenes, polycarbonates, methacrylics, phenols, polypropylene, polyolefins, such as polyolefin plastomers and elastomers, EPDM, and copolymers of ethylene, propylene and functional monomers.
Yet another embodiment is the composition of discrete carbon nanotubes in a plasticizer further mixed with at least one thermoset polymer, preferably an epoxy, or a polyurethane. The thermoset polymers can be selected from but is not limited to epoxy, polyurethane, or unsaturated polyester resins.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions describing specific embodiments of the disclosure.